FILM of a replica terror bomb was shown at the trial of men accused of the July 21 plot yesterday.

Explosives expert Clifford Todd was giving evidence as the jury saw footage of a controlled blast at a test site.

The high-speed video showed debris shooting up from a bomb of hydrogen peroxide mixed with chapatti flour.

Mr Todd said the film revealed a "bellshaped shimmer" in the air.

"That is the shockwave produced by the main explosive," he added.

Mt Todd's team conducted a series of test explosions using different combinations and concentrations of materials. Prosecutor Nigel Sweeney QC asked: "What did it tell you about the actual devices used on 21/7?"

Mr Todd replied: "What you had was a viable high explosive using flour and hydrogen peroxide."

Jurors heard the ratio and concentrations allegedly used on July 21 successfully exploded on every occasion at the Fort Halstead lab in Kent. The court heard the July 21 devices used the high-explosive TATP as a detonator.

The defendants have claimed the detonator had been set so as it did not explode the main charge.

Lab tests revealed TATP detonated the mixture at the "best" ratio.

It is claimed only "good fortune" stopped the TATP detonator igniting.